Shokeisareta Seijo wa Shiryou to Natte Maimodoru

Serena is a former orphan who has been given the skill of sainthood and lives in the royal palace. However, the prince and his mistress, the viscountess, dislike Serena and execute her on charges of being a false saint. After her death, she wakes up in a dark cave. But she cannot feel her body. Yes, she had become a pale, luminous, translucent sphere, endowed with reason! She is a kind of demon, a being composed only of spirit, but she survives thanks to her natural optimism.